How to Control Surface Roughness in 3D Printing Projects
Introduction
In the world of 3D printing, the quality of the final part is not just about functionality but also about appearance. One key factor that determines how well a 3D-printed part performs and looks is its surface roughness. Whether you’re designing a component for aerospace, automotive, or medical use, surface roughness can make a significant difference in how well a part meets its requirements. This blog will break down what surface roughness is, how it’s measured, and the factors that influence it, offering a comprehensive guide to understanding and managing surface roughness in 3D printing.
What is Surface Roughness in 3D Printing?
Surface roughness in 3D printing refers to the small, irregular deviations from an ideal smooth surface on the printed part. These deviations are often caused by the nature of the 3D printing process itself, including the layering of material and the precision of the machine.
The roughness of a part’s surface is quantified using a number of metrics, the most common being Ra (Average Roughness) and Rz (Average Maximum Height).
- Ra (Average Roughness): This metric measures the average height of surface deviations from the ideal mean line. A lower Ra indicates a smoother surface.
- Rz (Average Maximum Height): This metric measures the height difference between the highest peak and the lowest valley in the surface profile.
For many industries, especially those involving functional parts like aerospace, automotive, and medical devices, a lower surface roughness is essential for ensuring parts perform well under stress, fit properly, and don’t accumulate dirt or cause wear over time.
Factors Influencing Surface Roughness
Several factors contribute to the roughness of a 3D-printed part. Understanding these factors can help engineers and designers control and optimize surface quality.
1. 3D Printing Technology
Different 3D printing technologies affect surface roughness in various ways:
Fused Deposition Modeling (FDM): In FDM, material is extruded layer by layer. The surface roughness tends to be higher due to the visible layer lines and the way the material is deposited. As the material cools and solidifies, it can leave behind a rough texture. This is especially noticeable in materials like ABS, which are more prone to warping and inconsistency during cooling.
Stereolithography (SLA): SLA uses a laser to cure liquid resin, layer by layer, into a solid. The result is generally a much smoother surface, as the resin cures to a finer detail and doesn’t leave the same visible layer lines as FDM printing.
Selective Laser Sintering (SLS) and Direct Metal Laser Sintering (DMLS): Both SLS and DMLS use a laser to fuse powdered material into solid form. While these technologies can produce durable parts, the powder particles can cause roughness, especially in the “as printed” condition. For SLS, powder adhesion is a key factor, and this can result in rougher surfaces compared to SLA or FDM.
2. Material Properties
The material used in 3D printing plays a critical role in surface finish. For example:
PLA (Polylactic Acid): PLA is known for its smoother surface finishes compared to other materials like ABS. PLA is less likely to exhibit layer lines due to its more consistent extrusion properties.
ABS (Acrylonitrile Butadiene Styrene): ABS tends to show rougher finishes. It’s also more prone to warping, which can add to the irregularities on the surface. Parts made from ABS often require additional post-processing to improve surface smoothness.
Nylon, Polycarbonate, and Other Engineering Plastics: These materials can exhibit a wide range of surface qualities, with some requiring chemical or mechanical smoothing to achieve the desired finish.
3. Layer Height and Resolution
The layer height and resolution settings used during printing significantly influence surface roughness.
Smaller Layer Heights: Using smaller layer heights results in thinner layers, which makes the transition between layers less visible and the overall surface smoother. However, this also increases printing time and complexity.
Higher Resolution: Higher resolution settings allow for finer details, which can reduce the visibility of the layer lines. This improves the surface quality but also increases the computational power and time needed for printing.
4. Post-Processing Techniques
After printing, several post-processing methods can be used to improve surface smoothness:
Sanding and Polishing: These are the most common mechanical post-processing techniques. Sanding can smooth out rough areas, and polishing adds a glossy finish.
Chemical Smoothing: Techniques like chemical vapor polishing are used to smooth out the surfaces of parts, especially in technologies like SLS. The part is exposed to a chemical vapor that melts the surface slightly, filling in small rough areas for a smoother finish.
Plating and Coating: For certain applications, electroplating or coating a part with a smooth, hard layer can significantly reduce roughness and improve the finish.
Common Surface Roughness Values for Different 3D Printing Technologies
To help clarify what to expect from different 3D printing methods, here’s a breakdown of typical surface roughness values:
| Technology | Material | Ra (µm) | Rz (µm) |
|---|---|---|---|
| FDM | PLA | ~65 | ~200 |
| SLA | Industrial White Resin | 1.5 | 10.1 |
| SLS | PA 12 (as printed) | 10-12 | 59.9-69.4 |
| DMLS | Metal Parts | 7 | 35 |
As shown in the table, SLA generally produces the smoothest surface finishes, while FDM tends to result in rougher surfaces due to its layer-by-layer extrusion method. SLS and DMLS have intermediate values, with DMLS being especially variable depending on the specific metal used.
Conclusion
Surface roughness is more than just an aesthetic consideration in 3D printing; it has functional implications for a part’s performance. Whether it’s affecting the aerodynamics of an automotive part, the fit of a mechanical component, or the comfort of a medical device, understanding and controlling surface roughness is key to achieving high-quality 3D-printed parts.
By considering factors like printing technology, material choice, layer height, and post-processing techniques, engineers in ProtoSoon can optimize your 3D prints for better surface finishes.